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Abstract

This paper presents a new technique to generate microwave signal using an electro-absorption modulator (EAM) integrated with a distributed feedback (DFB) laser subject to optical injection. Experiments show that the frequency of the generated microwave can be tuned by changing the wavelength of the external laser or adjusting the bias voltage of the EAM. The frequency response of the EAM is studied and found to be unsmooth due to packaging parasitic effects and four-wave mixing effect occurring in the active layer of the DFB laser. It is also demonstrated that an EA modulator integrated in between two DFB lasers can be used instead of the EML under optical injection. This integrated chip can be used to realize a monolithically integrated tunable microwave source.

Figures (11)

Fig. 1 Experimental setup for microwave signal generation using an EML under external optical injection at the wavelength of λ1. The experimental setup using two external tunable lasers would be used in Section 3.

Fig. 2 (a) Cross-section structure diagram of the EML. (b) Measured spectrum of the microwave signal generated in the EAM. (c) Measured spectrum of the beat signal in the high-speed photodetector. The wavelength of the tunable laser was tuned to be about 7.5GHz higher than that of the DFB laser.

Fig. 6 Measured magnitudes of the beat signal between the lightwaves from the DFB laser and the tunable laser at different injection wavelengths (closed circle). Opened circle indicates the results when the DFB laser beam is replaced by the light beam from another tunable laser. The frequency response (solid line) measured by microwave network analyzer is also plotted in the figure for comparison.

Fig. 9 Measured spectra of the microwave signals generated in the modulator reversely biased at different voltages, where the bias current of the DFB laser and the injection optical wavelength are kept unchanged.